Inflatable airbag and a method of manufacturing the same

ABSTRACT

The invention relates to an inflatable gas bag ( 10 ) for an occupant restraint system of a vehicle, in particular of a motor vehicle. In order to avoid the formation of creases in the inflated state, which occurs with conventional gas bags and in order to be able to employ more lightweight textile materials for the manufacture of a gas bag, the gas bag ( 10 ) consists of a multilayered textile composite material which comprises at least one layer of a textile material and one layer of a polymer material whose melting range is lower than the melting range of the textile material. The textile composite material is formed into a specified three-dimensional shape which is to develop during inflation of the gas bag ( 10 ), and the individual layers of the textile composite material are joined together in this three-dimensional shape.

FIELD OF THE INVENTION BACKGROUND OF THE INVENTION

The invention relates to an inflatable gas bag for an occupant restraintsystem in a vehicle and a method for manufacturing such a gas bag.

Occupant restraint systems with gas bags, frequently also referred to asairbags, which are automatically inflated in the case of a seriousaccident are nowadays installed in a plurality of passenger cars both onthe driver's side and on the passenger's side in order to possiblyavoid, in the case of a serious frontal impact of the vehicle, potentialhead and chest injuries of the vehicle occupants which are seated in thefront. Such systems which essentially consist of a mostly pyrotechnicalgas generator and a gas bag as well as of the associated controlelectronics are increasingly employed in the lateral area of passengercars in order to dampen and distribute the forces acting upon thevehicle in the case of a side impact over a larger area and thusdecrease the injury hazard for the vehicle occupant who is seated on theimpact side. Such laterally arranged impact protection systems with gasbag, which are also referred to as sidebags, are, for example,accommodated in the vehicle doors or in the backrests.

On the basis of the predominantly positive experience gained with suchimpact protection systems which comprise a gas bag the trend exists toemploy such systems on a wider scale in trucks and buses as well.

Depending on the task which an occupant restraint system of theinitially mentioned type is to fulfill, the gas bag in its inflatedstate must have a precisely defined shape in order to achieve theoptimum effect. The so-called driver airbags in their inflated stateare, for example, approximately balloon-shaped, while the so-calledpassenger airbags in their inflated state are approximatelycushion-shaped. Side airbags, in turn, frequently still have intricateshapes in order to be able to comply with the requirements imposed onthem.

In addition, gas bags must fulfill two contradictory requirements: Onthe one hand they must be inflatable as rapidly as possible whenrequired; on the other hand they have to provide as large a distance aspossible between the vehicle occupant to be protected and the objectwith which the vehicle occupant must not collide. While the firstrequirement calls for a small gas bag volume, a relatively large gas bagvolume is the result of the second requirement. The existence of impactprotection systems with a gas bag, however, is only justified if theirprotective effect is as good as possible so that nowadays large gas bagvolumes are preferred in order to achieve an optimum protective effect.

Conventional gas bags consist of two or more individual textile partswhich are cut from textile flat material and subsequently sewn together.Accordingly, two circularly made-up two-dimensional textile parts aregenerally sewn together for a driver's airbag. Upon inflating theseconventionally manufactured gas bags into their three-dimensional statewhich they must assume in order to achieve the desired protectiveeffect, creases occur in particular in the seam area, which extendperpendicular to the seams. These creases result in high stress peaks inthe seam area which is already weakened by the seam. In order to avoidbursting of the gas bag in the seam area under load, very heavy fabricsare used in the manufacturer of the gas bag. These heavy fabrics inconjunction with the relatively large gas bag volume selected forachieving a good protective effect result in conventional gas bags beingrelatively heavy. In order to nevertheless ensure the rapid inflationwhen necessary, larger gas generators have to be employed which arecapable of correspondingly rapidly accelerating the relatively largemass of the gas bag. Large pyrotechnical gas generators in turn aredisadvantageous in that during inflation the temperature of the gasdeveloped by the gas generator reaches very high values and that thesehigh temperatures can affect the gas bag and destroy its fabric. Inaddition, a gas bag with a larger mass unfolds only later due to itshigher inertia so that the hot gases developed by the gas generator actlonger on the still folded fabric which is located near the gasgenerator. In order to not destroy the gas bag fabric as a result ofthis bombardment with the combustion gases great yarn thicknesses(approx. 250 to 700 dtex) are employed which ensure that the fabric doesnot fail even then when glowing particles impinge on the fabric andindividual threads start melting.

SUMMARY OF THE INVENTION

The relatively large mass of conventional gas bags must, of course, notonly be accelerated but also stopped again at the end of the inflationprocess. In this case, too, great loads occur in particular in the seamarea which must be compensated by correspondingly reinforced seams or bymultiple seams. These measures again result in an increase in the gasbag weight.

The conventionally used heavy fabrics not only have dynamicdisadvantages but, in addition, enforce a relatively large packingvolume due to the fact that they are also mostly relatively rigid. Theseam areas are naturally particularly rigid and can therefore causeundesired injuries such as, for example, skin grazes of the occupant tobe protected if the occupant assumes a so-called out-of-positionattitude while the gas bag unfolds. Any attitude which does notcorrespond to the optimum position relative to the gas bag istechnically termed “out-of-position”, for example an occupant who isseated too close to the gas bag or lateral to it. In suchout-of-position attitudes the risk to be fully hit by a rigid seam areais particularly high.

In order to fulfill its protective function the gas bag must comply withtwo additional and also contradictory requirements: As already mentionedit must be inflatable as rapidly as possible. This requirement cangenerally be met only with a very tight gas bag because only then willit be ensured that the gas developed by the gas generator is completelyused for inflating. On the other hand, the gas bag in the inflated statemust dampen the impact of an occupant of the vehicle. To this end thegas bag must allow a defined venting of its gas filling becauseotherwise the colliding occupant would bounce back. Therefore, in theside facing away from the vehicle occupant, conventional gas bags areprovided with openings which can have a diameter of up to 50 mm. Theseopenings are also referred to as “vents”. Because these openings are notclosed during inflation, a considerable portion of the gas developed bythe gas generator escapes so that the gas generator must have acorrespondingly more powerful, i.e. larger, design in order to be ableto reliably inflate the gas bag. Large gas generators, however, resultin the above already explained thermal stresses of the gas bag fabric.

Finally, the conventionally employed heavy fabrics are not particularlytight because of the relatively great yarn thicknesses used so thatthese fabrics must generally be additionally coated in order to obtainthe required tightness. The coatings, however, often have the problem ofa poor ageing stability so that the satisfactory function of the gas bagmight possibly no longer be ensured after many years.

Although known impact protection systems with gas bags decisivelyimprove the occupants' safety, thus justifying their increasinglylarge-scale use, these systems still have quite a number of drawbackswhich prevent an even better protective effect and moreover increase themanufacturing costs of conventional systems.

The invention is based on the object to improve conventional impactprotection systems with gas bags in such a manner that with an increasedprotective effect as many of the above mentioned problems as possibleare solved.

According to the invention this object is solved by an inflatable gasbag for an occupant restraint system, which consists of a multilayeredtextile composite material which comprises at least one layer of atextile material and one layer of a polymer material whose melting rangeis lower than the melting range of the textile material, with thetextile composite material being formed into a predeterminedthree-dimensional shape-which-is to develop during inflation of the gasbag and the individual layers of the textile composite material havebeen joined together only in the three-dimensional shape of the gas bag.

The gas bag according to the invention therefore differs quiteessentially from the previously known gas bags: During its manufactureit is already formed into the three-dimensional shape which it is toassume in the inflated state. The inventive gas bag is heat set in thisthree-dimensional shape by means of thermal treatment. Contrary toconventional gas bags which are combined or sewn together, respectively,from two-dimensional flat members, the described crease formation nolonger occurs during inflation of the inventive gas bag, which inconventional gas bags causes dangerous stress peaks.

Due to the fact that the inventive gas bag is formed into itsthree-dimensional functional state during manufacture, the strength ofits material can be selected considerably lower compared to thepreviously employed materials because the stress distribution in the gasbag material of a gas bag according to the invention is much moreuniform. According to the invention considerably more lightweighttextiles can thus be employed as gas bag material. In addition to thepreviously described advantage of a more uniform stress distribution,forming the inventive gas bag into its three-dimensional functionalstate during manufacture also makes it possible to reduce the gas bagvolume as compared to conventional gas bags having the same protectiveeffect because a gas bag according to the invention can, for example, bepreformed into an egg-shaped configuration and in this manner bridge thesame distance for which a ball-shaped gas bag with a correspondinglylarger volume is conventionally required.

The inventive use of a multilayered textile composite material resultsin further advantages: The now employable textile materials of lighterweight need no longer be coated but rather obtain their tightness bymeans of the layer of polymer material which is but joined with thelayer(s) of textile material in the desired three-dimensional shape ofthe gas bag. By means of suitable temperature control during the joiningprocess the resulting textile composite material can also be given adefined gas permeability which can even be adjusted so as to be locallydifferent. For example, on the side of the gas bag facing away from theoccupant areas with a higher gas permeability can be generated so thatthe conventional vent orifices can be dispensed with. Due to theomission of the conventional vent orifices, the inflation losses of thegas bag according to the invention are, on the one hand, much smaller sothat the use of a smaller gas generator becomes possible and, on theother hand, the weight of the gas bag is again reduced because theconventional vent orifices are seamed by one or several seams forstability reasons.

Furthermore the inflation dynamics of the gas bag according to theinvention can be influenced by a locally different adjustment of thepermeability of the textile composite material, i.e. the shape can beprecisely controlled during inflation. Thereby, for example, thepreviously occurring and undesired “mushrooming” (mushroom-type ejectionof the gas bag in the initial phase of the inflation process) can beprevented. Restraining straps within the gas bag as were previouslyemployed to prevent “mushrooming” can be dispensed with in the inventivegas bag, which again makes same more lightweight. The preciselydefinable permeability of the textile composite material employedaccording to the invention additionally permits a controlled venting ofthe inflated gas bag and thus a nearly linear damping of the motion ofthe colliding occupant. In other words, the inventive gas bag can beimparted an accurately defined deformation energy absorption.

In summary, the inventive gas bag even in its simplest configurationoffers the following advantages:

While the previously used gas bag fabrics, e.g. for a gas bag on thedriver's side, have masses per unit area ranging from approx. 180 g/m²to 220 g/m² the multilayered textile composite material used accordingto the invention in the molded state has a 30 to 50 per cent lower massper unit area.

While the previously used gas bag fabrics have tensile strengths rangingfrom approx. 1,800 to 2,200 N/5 cm (to DIN 53857, Part 1) themultilayered textile composite material of the inventive gas bag isrequired to have only approx. 25 to 50 per cent of this tensilestrength.

While the previously employed yarn thicknesses amount to approx. 250 to700 dtex the yarn thicknesses of the textile material employed for theinventive gas bag may range from approx. 20 to approx. 40 dtex.

The gas bag according to the invention can be brought into any shapewhich is desired from the point of view of safety while at the same timeminimizing its volume.

Due to its superior design the gas bag according to the invention isgenerally considerably more lightweight than previous gas bags and thuspermits the use of smaller gas generators.

The gas bag according to the invention requires a considerably lowerpacking volume which, for example, allows the vehicle manufacturers toaccommodate gas bags with large volumes also in smaller visually moreattractive steering wheel hubs as are generally used in sports steeringwheels.

According to a preferred configuration in terms of manufacture andfunction the inventive gas bag consists of several portions each ofwhich is formed into one part each of the three-dimensional shape of thegas bag and which are joined together in the three-dimensional shape ofthe gas bag, in particular by lap sealing. According to thisconfiguration a gas bag intended for the driver's side is preferablyformed by combining two e.g. approximately hemispherical portions. Sucha configuration permits the use of a textile material for the side ofthe gas bag facing the occupant which is different from that facing awayfrom the occupant so that an optimum adaptation of the textile materialto different requirements can be effected. In order to join theindividual partial portions, all known joining techniques (with orwithout an inserted auxiliary tape) can generally be used. Theindividual portions can also be glued or sewn together. The latter typeof joining, however, is the one considered the least advantageous.

The layer of a polymer material provided according to the invention canbe constituted by a plastic film or by a plastic fleece. The layer ofpolymer material itself can consist of several layers, for example, oftwo thin layers of a melting adhesive between which a plastic film isarranged. The layers of melting adhesive can, in turn, be formed by thinfleeces (so-called hotmelt fleece). With a multilayered structure ofthis type of the polymer material layer the joint area remains soft andflexible also after hot sealing because the central layer of the polymermaterial need not be heated to the flow condition. Instead, only thethin melting adhesive layers are heated to the flow condition andprovide for the desired intimate interconnection of the textilecomposite material.

According to a particularly preferred embodiment of the inventive gasbag the textile composite material comprises at least two layers oftextile material between which the layer of polymer material isarranged. This embodiment makes it possible to select the textilematerial on the gas bag inner surface different from the textilematerial on the gas bag outer surface and, thus, to better adapt it tothe different requirements (inner surface temperature resistance, outersurface softness, etc.). In addition, this embodiment also makes itpossible to make the properties of the inventive textile compositematerial more isotropic by joining together the two layers of textilematerial with an opposite twist at a defined angle in order tocompensate, for example, the biaxial elongation differences. It goeswithout saying that also three or more layers of textile material can beused in order to achieve an even better isotropy. One layer of polymermaterial is always arranged between two layers each of textile material.In order to achieve a better isotropy the individual layers of textilematerial need not consist of different materials, but may, of course,consist of the same textile material.

In the case of the inventive gas bag, a knitted fabric, a warp-knittedfabric, or a woven fabric can be used. Preferably, however, knittedfabrics, i.e. warp-knitted or knitted fabrics, are used because withknitted fabrics a very good isotropy can be achieved in thethree-dimensional functional state of the gas bag, even in the case ofonly a few textile layers. Woven fabrics, however, always have a warpand weft direction so that a high isotropy is difficult to obtain.

In order to facilitate recycling of the gas bag according to theinvention, the layers of textile material and the polymer materialpreferably consist of the same material, for example, of polyamide or ofpolyester.

The initially mentioned problems of conventional impact protectionsystems with gas bags are also solved by an inventive method for themanufacture of an inflatable gas bag, wherein a layered structure of atleast one layer of textile material and one layer of polymer materialwhose melting range is lower than the melting range of the textilematerial is brought into the desired three-dimensional shape whichdevelops on inflation of the gas bag or a portion of said shape bymeans; of heated forming tools and is thermally set in this state andsimultaneously laminated to a textile composite material. This method isparticularly well suited for the manufacture of a previously describedinventive gas bag.

In the manufacturing method according to the invention the layeredstructure whose layers are not yet securely joined to one another isbrought into the desired three-dimensional shape which may correspond tothe complete gas bag or to a portion therefrom between usually twoheated forming tools and is thermally set in this state andsimultaneously laminated to a textile composite material. The methodaccording to the invention is thus a three-dimensional textilelaminating and molding method. In the inventive manufacturing method forgas bags it must be ensured that no excessive compacting pressure isgenerated between the forming tools so that the generating textilecomposite material maintains its textile properties as far as possible.

The thermal setting of the obtained three-dimensional shape is effectedby selecting the temperature of the forming tools such that the textilematerial does not begin to melt or is damaged but is thermally set inthe desired three-dimensional shape. If required, thermal setting can beassisted by chemical auxiliary agents and/or mechanical rubbingmovements of the forming tools. Due to the laminate generated in thismanner the textile composite material of the gas bag according to theinvention has an extremely high strength with a low weight. The mass perunit area of the employed textile composite material in thethree-dimensional functional state preferably ranges from approx. 100g/m² to approx. 150 g/m².

According to the invention, melting starts only with the layer ofpolymer material in order to achieve an intimate connection with thetextile layer or the textile layers. The commencement of melting of thepolymer layer can be controlled in such a manner that, at the same time,the permeability of the generating textile composite material isaccurately adjusted. The temperature can thereby be controlled in alocally different manner so that locally different gas permeabilitiescan be obtained. In addition to or as an alternative to the possibilityof adjusting the gas permeability of the gas bag by means of controllingthe temperature in the inventive manufacturing method, it is alsopossible to perform a specific mechanical perforation of the layeredstructure or the generating textile composite material, e.g. by means ofa forming tool provided with needles, during the forming, heat settingand laminating process.

If the gas bag is to be combined from several portions, these individualportions are joined together in the manufacturing method according tothe invention in the desired three-dimensional shape, preferably bymeans of lap sealing. Compared to the previously used sewing techniquewhich yields a maximum of 50 to 60 per cent of the fabric strength inthe seam areas at least almost the strength of the remaining textilecomposite material is achieved also in the joint areas by means of lapsealing. This leads to a significant weight saving for a gas bag whichis manufactured in accordance with the inventive method. In addition,the edges of the individual portions of the gas bag which aremanufactured in accordance with the inventive method can be exactlyseamed with the seam not extending outwardly or inwardly as hitherto butbeing flush with the three-dimensional shape of the gas bag. Therefore,no protruding seam is generated when joining the individual portions butthe joint area is also located within the enveloping surface of the gasbag. In this manner a precise lap sealing of individual portions becomespossible. In addition a joint obtained by lap sealing is stronger andmore lightweight than a conventional sewn seam.

The inventive manufacturing method permits the individual textile layersto be stretched during the forming process up to an also locally definedresidual elasticity. As already explained in conjunction with the abovedescribed gas bag according to the invention the inflation dynamics canthereby be precisely influenced. Moreover, stretching of the textilelayers results in an increase of the tensile strength of the textilecomposite material.

The inventive manufacturing method can be carried out with textilematerials made from all commercially available synthetic fibres but alsowith textile materials from natural fibres, e.g. mercerized cotton. Itis of importance that the melting range of the polymer layer(s) islower, preferably only slightly lower, than the melting range of thetextile material. A number of successful test samples has already beenmanufactured both from polyamide and from polyester textile materials.In general, such textile materials have a melting range from approx. 210to 240° C. The temperature to be selected in the inventive manufacturingmethod when using such textile materials is therefore within a range ofbetween approx. 180 and 210° C. so that the textile material will not bedamaged, the polymer material layer, however just begins to melt.

The above described gas bags with their advantageous properties can bemanufactured by means of the inventive method. In spite of thegeneration of a multilayered textile composite material themanufacturing costs are, due to the significantly lower mass per unitarea, considerably lower than the manufacturing costs for conventionalgas bags which must use the heavier textile materials.

Although the just described manufacturing method has been explainedabove with reference to gas bags for impact protection systems, it isobvious for those skilled in the art that this manufacturing method canvery advantageously be employed for other formed parts made from textilematerials as well. For example, textile formed parts can be manufacturedfor work, sports, leisure clothing or for containers of textilematerials such as rucksacks or bags. One sample application would be tomake clothing shoulder sections which are to be rainproof but breathingby means of the inventive method. In this manner the hitherto seam onthe shoulder which leads to tightness problems or which has to be sealedseparately with a considerable amount of effort can be omitted. Themethod according to the invention is therefore particularly suited forthe manufacture of formed textile parts which are to be permeable forwater vapour in one direction in order to be able to emit the watervapour which is generated when sweating during heavy physical labour andwaterproof in the other direction in order to provide, for example, aprotection against rain.

The invention will be explained in the following with reference toschematic drawings of a preferred embodiment of an inventive gas bag, inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, FIG. 1a, and FIG. 1b shows a conventional gas bag for an impactprotection system in a vehicle;

FIG. 2 shows a gas bag joined from two portions, which is manufacturedaccording to the invention;

FIG. 3 shows the joint area (detail 3) between the two portions of thegas bag from FIG. 2 as a section and in an enlarged illustration;

FIG. 4 shows the section through a textile composite material usedaccording to the present invention;

FIG. 5 shows the joining of two gas bag halves manufactured according tothe invention;

FIG. 6 shows the manufacture of a gas bag half according to theinvention; and

FIG. 7 shows an example of a manufacturing tool for the manufacture of agas bag according to the invention consisting of only one part.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a conventionally manufactured gas bag 1 of an impactprotection system known from the state of the art which is arranged onthe driver's side in a motor vehicle, also referred to as a driverairbag. The gas bag 1 consists of an upper half 2 which faces towardsthe driver and a lower half 4 which faces away from the driver. The twohalves 2, 4 are joined together by means of a sewn seam 5 which in theillustrated example is constructed as a double seam. The sewn seam 5forms a seam which projects essentially at right angle from the gas bag1 and which according to the detail drawings 1 a and 2 a either projectsinto the interior of the gas bag 1 or outwardly from the gas bag 1. Bothhalves 2, 4 are made-up of circular disk-shaped textile parts of flattextile material.

From FIG. 1 which shows the gas bag 1 in the inflated state it canclearly be seen that the deformation which occurs during the inflationprocess of the flat textile parts which constitute the two halves 2 and4 into the three-dimensional state a plurality of creases 6 is generatedin the joint area of the two halves 2 and 4 as well as creases 7 whichextend from the connecting cone of the gas bag 1 over its lower half 4.The creases 6 extend essentially perpendicularly to the sewn seam 5 and,like the creases 7, result in undesired stress peaks in the gas bagfabric.

In the lower half 4 of the gas bag 1 an orifice or opening 8 can also beseen through which the gas can be vented upon impact of the vehicleoccupant on the gas bag 1. If required, several of such openings 8 areprovided. Due to the fact that these openings 8 are not closed duringinflation of the gas bag 1 a considerable amount of the filling gaswhich is actually intended for inflation of the gas bag is alreadyvented during the inflation process.

The gas bag 1 shown in FIG. 1 is attached to a gas generator (not shownherein) which is accommodated in the hub of a steering wheel 9.

FIG. 2 shows a gas bag lo according to the invention in the inflatedstate. Contrary to the just described conventional gas bag, two halves12 and 14 of the inventive gas bag 10 shown in FIG. 2 have been formedinto the desired three-dimensional shape and thermally set in thisthree-dimensional shape by means of the method according to theinvention. Contrary to the state of the art the two halves 12 and 14 arenot joined together by means of a sewn seam but by a lap seal 16. A lapseal of this type can, for example, be obtained by means of ultrasonicsealing. The lap seal 16 has a very high strength and causes only aminor material thickening in the joint area so that the previouslyexisting injury risk due to projecting and/or rigid seams is minimized.The way of manufacturing gives the inventive gas bag 10 a shape free ofcreases in the inflated state. S1 identifies the functional distancewhich is obtained in the inflated state between an area defined by thesteering wheel rim 18 and the maximum extension of the gas bag 10 in thedirection towards the vehicle occupant.

FIG. 3 and FIG. 4 show in more detail the structure of the textilecomposite material of which the inventive gas bag 10 consists. Thetextile composite material of the illustrated embodiment comprises threelayers and consists of two layers 20, 22 of textile material betweenwhich one layer 24 of polymer material is arranged which herein isformed as a plastic film. In the joint area of the two halves 12 and 14of the gas bag 10 the layer 24 of polymer material is brought into aflowable condition, e.g. by means of ultrasound, so that the polymermaterial penetrates the layers 20 and 22 of textile material and is thuscombined with the respective adjacent textile material layer of theother half 12 or 14. After cooling down of the polymer material whichhas been brought into the flow condition in the overlap area of the twohalves 12 and 14, the two halves 12, 14 are securely joined together bymeans of the generated lap seal 16. Due to the fact that the thicknessof the layer 24 of polymer material is reduced during heat sealing thearea of the lap seal between the halves 12 and 14 is only slightlythicker than the adjacent textile composite material.

FIG. 4 again shows a section through the structure of the textilecomposite material. The layers 20 and 22 of textile material may differfrom each other, i.e. they may consist of different textile materials.

The manufacturing of the gas bag 10 will now be described in more detailwith reference to FIGS. 5 and 6. In the manufacture of the gas bag 10 anapparatus is used which may be a heated female die tool 26 and an alsoheated male die tool 28 (see FIG. 5). Between the two forming tools 26and 28 a layered structure 30 is first placed which in the shown exampleconsists of two layers 20, 22 of warp-knitted textile material and alayer 24 of polymer material in the form of a plastic film which isarranged between them. Initially, the individual layers of the layeredstructure 30 are not securely joined together.

In a next step the two heated forming tools 26, 28 are moved intocontact with each other in order to bring the layered structure 30 intothat form which the gas bag 10 or a portion of same is intended toassume later in the inflated state. FIG. 5 shows the closed condition ofthe two forming tools 26 and 28 with reference to an example for themanufacture of an upper half of a driver's airbag. During the closingmovement of the forming tools 26 and 28 it may be useful to apply avacuum to the female die tool 26 in order to assist the sliding in ofthe layered structure 30 into the forming tool 26. By maintaining thelayered structure 30 under a defined counterstress during the closingmovement of the two forming tools 26 and 28, the layers 20 and 22 oftextile material which are arranged between the two forming tools 26 and28 can be stretched up to a predetermined residual elongation property.

It is of importance that in the closed end position of the two formingtools 26 and 28 no excessive compaction pressure is exerted onto thelayered structure 30 so that its textile properties are maintained asfar as possible. Therefore, a defined gap whose gap width depends on thestructure of the respective layered structure 30 is provided between theheating layers 32 and 34 of the two forming tools 26 and 28.

In the position of the forming tools 26 and 28 as shown in FIG. 5 thelayered structure 30 is simultaneously thermally set and formed into atextile composite material in the three-dimensional shape which isspecified by the forming tools 26 and 28. This is achieved in that thetemperature of the forming tools 26 and 28 is selected in such a mannerthat, on the one hand, the two layers 20 and 22 are heated only to suchan extent that, in a similar manner to an ironing process, they assumethe shape as specified by the forming tools 26 and 28 free of creases,and that on the other hand, however, the temperature is sufficient tojust start melting the polymer intermediate layer 24 at the two layers20 and 22 of textile material. It has proven to be advantageous toselect the polymer material of the layer 24 in such a manner that itsmelting range is only slightly, i.e. approx. 20 to 40° C., below themelting range of the textile material.

After the described forming and heat setting process the obtained formedtextile part is brought exactly into the desired dimension by means of aring 36 which is arranged concentrically with the male die tool 28 and acircumferential groove 38 which is provided in the female die tool 26 byengaging a blade (not shown) into the circumferential groove 38 forcutting off any surplus margin. Alternatively, this exact dressing canalso be carried out e.g. by means of a resistance wire embedded in themale die tool 28, which is briefly heated and thereby melts off thesurplus margin. After the dressing operation the two forming tools 26and 28 are opened again and the formed textile part, in the shownexample one half of a gas bag, can be removed. The textile formed partis as soft and supple as a textile piece and can therefore be foldedextraordinarily well.

FIG. 6 shows how two separately manufactured gas bag halves are joined.For this purpose a lower gas bag half 40 is first placed into a femaledie tool 26′ and then an upper gas bag half 42 turned to the inside isplaced upon the lower gas bag half 40. An annular loose part 44 made ofsteel or PTFE is arranged in the joint area between the upper gas baghalf 42 and the lower gas bag half 40 so that the margins of the uppergas bag half 42 and the lower gas bag half 40 overlap on the radiallyouter circumferential surface of this loose part 44. This isschematically indicated in FIG. 6 by a small gap between the overlappingmargins.

Subsequently the two overlapping margins of the upper and lower gas baghalf are heat sealed to one another, for example by means of anultrasonic sonotrode 46 and the loose part 44 as a counter support. Thetwo gas bag halves 40 and 42 are then joined to form the gas bag 10 andafter opening of the forming tools 26′, 28′ only the loose part 44 hasto be removed through the gas generator connecting port of the formedgas bag 10.

With the described manufacturing method gas bag halves 40 and 42 with anaccurately defined gas permeability can be manufactured in that thetemperature of both forming tools 26 and 28 is accurately, also locally,controlled. Alternatively or additionally, the female die tool 26 can beprovided with needles which later perforate the generated textilecomposite material (not shown). It is therefore possible to manufacturegas bags 10 with a gas bag shape which is individually matched to acertain vehicle type and locally different gas permeabilities by meansof the described manufacturing method so that the impact energy of avehicle occupant can be optimally absorbed and dampened. In addition,the filter effect of the gas bag 10 can be adjusted without specialnozzles in such a manner that both an optimum dynamic behaviour duringthe inflation process is achieved and the ingress of harmful gases intothe area of the occupants is prevented to a large degree.

Finally, FIG. 7 shows a possibility of manufacturing a gas bag 10 in onepart and without heat sealing joint. For this purpose the layered objectis drawn or blown, respectively, into a hollow mould 48 and hot air isthen blown through the gas generator connecting port into the gas bag 10so that the individual layers of the layered structure fit snugly to thehollow surface of the hollow mould 46 and are thermally set there andlaminated to the composite material. Cooling air is then blown inthrough the gas generator connecting port 50 and the completed gas bag10 is removed.

What is claimed is:
 1. An inflatable gas bag for an occupant restraintsystem in a vehicle, said gas bag comprising a thermally moldedmultilayer textile composite comprising two layers of textile fabricmaterial and at least one layer of fusible polymer material disposedbetween said two layers, wherein the melting point of said fusiblepolymer material is lower than the melting point of said textile fabricmaterial and wherein said fusible polymer material has been fused tosaid textile fabric material in a predetermined three-dimensional shapesubstantially corresponding to the inflation profile of said gas bag. 2.The invention according to claim 1, wherein said gas bag comprises twoor more molded multilayered textile composites joined together in athree-dimensional shape.
 3. The invention according to claim 2, whereinat least two of said two or more molded multilayered textile compositesincorporate different textile fabric materials.
 4. The inventionaccording to claim 1, wherein said layer of fusible polymer materialcomprises a plastic film or fleece.
 5. The invention according to claim4, wherein said layer of fusible polymer material comprises a layer ofplastic film disposed within a melting adhesive.
 6. The inventionaccording to claim 1, wherein said two layers of textile fabric materialare different from one another.
 7. The invention according to claim 1,wherein said textile fabric material is selected from the groupconsisting of knitted fabrics, warp-knitted fabrics, and woven fabrics,and further wherein said fusible polymer material has been fused to saidtextile fabric material between forming tools.
 8. The inventionaccording to claim 1, wherein said textile composite is characterized bya mass per unit area of about 100 g/m² to about 150 g/m².
 9. Theinvention according to claim 1, wherein said gas bag has localizedregions of enhanced gas permeability.
 10. A method for manufacture of aninflatable gas bag for use in a vehicle restraint system comprising theconcurrent steps of: (a) fusing a polymer material to at least one layerof textile fabric material between forming tools to form a multilayeredtextile composite; and (b) thermally forming said multilayered textilecomposite into a three-dimensional shape corresponding to the desiredprofile of said inflatable as bag.
 11. The method as in claim 10,wherein two or more forming tools are utilized to form attachablethree-dimensional segments to said inflatable gas bag.
 12. The method asin claim 10, wherein said polymer material fused to said textile fabricmaterial comprises a film or fleece material.
 13. The method as in claim10, wherein said multilayered textile composite comprises two layers oftextile fabric material between which said polymer material is disposed.14. The method as in claim 13, wherein said two layers of textile fabricmaterial are different from one another.
 15. The method as in claim 10,wherein said at least one layer of textile fabric material is selectedfrom the group consisting of knitted fabrics, warp knitted fabrics andwoven fabrics.
 16. The method according to claim 10, wherein saidmultilayered textile composite is characterized by a mass per unit areain the range of about 100 g/m² to about 150 g/m².
 17. The methodaccording to claim 10, comprising the additional step of: (c)perforating localized areas of said multilayered textile composite. 18.The method according to claim 10, wherein said polymer material and saidtextile fabric material have the same chemical identity.
 19. Aninflatable gas bag formed by the method according to claim
 10. 20. Anautomotive restraint system comprising an inflatable gas bag accordingto claim
 19. 21. An automotive restraint system comprising an inflatablegas bag as set forth in claim 1.